The present invention concerns a transfer case or differential with a bevel-pinion shaft which is supported in a drive housing by two spaced and axially pretensioned angular-contact ball bearings and which drives via a bevel pinion and ring gear a differential unit mounted in the drive housing, axle shafts being supported in the differential unit which are operationally connected with each other via output and differential gears.
Such differential gear boxes permit the drive wheels of each axle shaft to roll in slip-free fashion at a different speed of rotation in travelling over a curved path. A bevel-pinion shaft or a drive shaft with a bevel gear drives a ring gear rotationally joined with the differential unit in the interior of which are mounted output and differential gears. While driving straight ahead, these differential gears in the differential unit are at rest so that both axle shafts turn at the same speed of rotation as the ring gear. Upon driving in a curved path, a difference occurs in the speed of rotation of the two axle shafts. In this case, the differential gears rotate and result in the fact that the increase in the speed of rotation of the one axle shaft compared to the speed of rotation of the ring gear is precisely as large as the decrease in the speed of rotation of the other axle shaft compared to the ring gear.
Such a generic differential gear box is described, for example, in the handbook xe2x80x9cRoller Bearingsxe2x80x94Computation and Designxe2x80x9d by W. Hampp, Springer-Verlag Berlin/Heidelberg/New York in Figure 88. The bevel pinion shaft is supported in this case via two spaced conical-roller bearings pretensioned in the axial direction. The pretensioning occurs as a result of the conical-roller bearings being moved toward each other in the axial direction via a threaded connection.
Disadvantageous here is that fact that due to the pretensioning of the conical-roller bearings, sliding friction develops between the end walls of the conical rollers and the edge surface of the bearing rings, which leads to wear of the conical rollers and edge surfaces. This wear, in turn, is responsible for loss in pretensioning of the bearing, as a result of which there occurs an increase in tooth play between the bevel pinion and the ring gear, with its negative consequences.
In connection with this, a differential gear box is known from U.S. Pat. No. 3,792,625, whose bevel-pinion shaft is supported by two spaced apart angular contact ball bearings. Such a bearing arrangement however does not meet the requirements for high performance drives and was therefore not useable from a technical standpoint. For one, the carrier teeth and also the rigidity are too small. Therefore it results in an uneven carrier stopping that lowers the service life of the drive and generates noise when the teeth of the bevel-pinion shaft and the ring gear mesh.
The present invention is therefore directed to developing an improved bearing arrangement for the bevel-pinion shaft of a differential.
According to the present invention, this problem is solved through the fact that the angular contact ball bearings are designed as unilaterally loadable double-row tandem angular-contact ball bearings, which each include a one piece inner bearing race and a one piece over bearing race and which face each other in an O-arrangement.
The advantages of the solution of the present invention compared to the classical solution with conical-roller bearings are the following:
Due to the substantially reduced frictional moment based on the lack of sliding friction in the bearing arrangement of the present invention, there necessarily also result reduced bearing temperatures and accordingly also a reduced oil-sump temperature. Thus, overall, better efficiency and a lower power loss of the bearing arrangement are attained. Upon installation of the bearing arrangement of the present invention in a motor vehicle, reduced fuel consumption is now possible as a result of the lower power loss. The approximately 40xc2x0 C. lower temperatures of the oil sump also make it possible that a lighter housing material, for example, a magnesium alloy can be employed for the differential housing which, in turn, makes itself felt in a saving of weight.
A further advantage is a reduced wear of the bearing, which amounts to only about {fraction (1/10)} of the wear for the classical solution. This reduced wear accounts for the avoidance of axial shifting of the bevel-pinion shaft along with the known negative increase in tooth play between the bevel pinion on the bevel-pinion shaft and the ring gear connected with the differential unit.
Further advantageous refinements of the solution of the present invention include that the races of a bearing exhibit respectively the same or a different diameter and the same or a different pressure angle.
According to a further feature, the bearing balls of both races of a bearing are guided in cages and have the same or a different diameter.
Preferably, the first double-row tandem angular-contact ball bearing positioned next to the bevel pinion on the bevel-pinion shaft is larger than the accompanying second bearing. This appropriate refinement is undertaken because the greatest loads both in the radial as well as in the axial direction need to be accommodated in the immediate vicinity of the bevel pinion.
Finally, it is preferred that the inner ring of the second double-row tandem angular-contact ball bearing is supported in the axial direction against a deformable sleeve. After adjustment for the desired pretensioning, this sleeve provides for the fact that the adjustment screw is likewise put under pretensioning through the action of a counter force. Spontaneous loosening of this threaded screw is therefore not possible.
The present invention is described in more detail on the basis of the following preferred embodiment.